1. Field of the Invention
The present invention relates to a polishing apparatus for polishing a workpiece such as a semiconductor wafer to a flat mirror finish, and more particularly to a multi-head type polishing apparatus having a plurality of top rings for holding workpieces with respect to a single polishing table.
2. Description of the Related Art
Recent rapid progress in semiconductor device integration demands smaller and smaller wiring patterns or interconnections and also narrower spaces between interconnections which connect active areas. One process available for forming such interconnections is photolithography. A photolithographic process requires that surfaces on which pattern images are to be focused by a stepper should be as flat as possible because depth of focus of an optical system is relatively small. It is therefore necessary to make surfaces of semiconductor wafers flat for photolithography.
One customary way of planarizing a surface of a semiconductor wafer is to polish the semiconductor wafer by a chemical mechanical polishing (CMP) process.
There has been known a multi-head type polishing apparatus which has a plurality of top rings for holding semiconductor wafers with respect to a single polishing table, and which can polish a plurality of semiconductor wafers simultaneously. In this multi-head type polishing apparatus, semiconductor wafers are mounted on respective top rings, and then all of the semiconductor wafers held by the top rings are simultaneously pressed against a polishing surface of the polishing table and polished. After polishing of the semiconductor wafers is conducted for a predetermined time, all of the top rings holding the semiconductor wafers are raised from the polishing table, and then all of the semiconductor wafers which have been polished are removed from the top rings. Thereafter, new semiconductor wafers are mounted on the top rings.
In the conventional multi-head type polishing apparatus described above, a plurality of semiconductor wafers are simultaneously polished, and loading and unloading (i.e. replacement) of the semiconductor wafers are simultaneously conducted. However, in the case where loading of the semiconductor wafers to be polished onto a plurality of top rings, and unloading of the semiconductor wafers which have been polished from the top rings, are automated, loading and unloading of the semiconductor wafers are necessary to be performed in a short time without a transfer error. However, in the multi-head type polishing apparatus, there has been no loading and unloading mechanism which can meet such requirements.
The conventional multi-head type polishing apparatus is a dedicated polishing apparatus for conducting only polishing of semiconductor wafers, and hence the semiconductor wafers which have been polished are transported to a next cleaning process by a movable container in which they are immersed in water to keep them from drying during transportation. However, in the method in which the polishing process and the cleaning process are separately carried out, cleanliness of a clean room tends to be impaired, and the polished semiconductor wafers need to be transported by an operator or a manually operated transportation device. Further, a large installation space is required for two kinds of apparatuses, i.e. a polishing apparatus and a cleaning apparatus that is used to carry out a subsequent cleaning process.
Therefore, in order to make a polishing process clean and reduce installation space of the apparatus, there has been demanded a multi-head type polishing apparatus which performs both a polishing process and a cleaning process therein, and is of a dry-in and dry-out type for introducing semiconductor wafers therein in a dry condition and removing polished and cleaned semiconductor wafers therefrom in a dry condition.
It is therefore an object of the present invention to provide a multi-head type polishing apparatus which can be used as a dry-in and dry-out type polishing apparatus, has a high processing capability per unit time and unit installation area for processing workpieces such as semiconductor wafers.
In order to achieve the above object, according to a first aspect of the present invention, there is provided a polishing apparatus having a multi-head, comprising: a polishing table having a polishing surface; a plurality of top rings for holding workpieces and pressing the workpieces against the polishing surface; a carousel for supporting the top rings and indexing the top rings; a rotary transporter disposed in a position which can be accessed by the top rings; and a pusher for transferring the workpieces between the rotary transporter and the top rings. The rotating transporter has a plurality of portions positioned on a predetermined circumference, from a center of rotation of the rotary transporter, for holding the workpieces, and the rotary transporter also has an indexing function for indexing the plurality of portions.
According to the present invention, it is possible to shorten time required to transfer workpieces to be polished, such as semiconductor wafers, to the top rings for thereby greatly increasing the number of processed workpieces per unit time, i.e., throughput.
According to a second aspect of the present invention, there is provided a polishing apparatus having a multi-head, comprising: a polishing table having a polishing surface; a plurality of top rings for holding workpieces and pressing the workpieces against the polishing surface; a carousel for supporting the top rings and indexing the top rings; a plurality of cleaning apparatuses for cleaning the workpieces which have been polished; a transfer mechanism for transferring the polished workpieces between the cleaning apparatuses; and a workpiece station having workpiece trays for holding the workpieces in a standby state, while the workpieces are cleaned in a plurality of stages in the cleaning apparatuses or before the workpieces are cleaned.
According to the present invention, some of workpieces can be placed in a standby state in workpiece supports (workpiece trays) of a workpiece station before being processed in a subsequent process.